The Contractor shall immunize mice with antigens, predominantly membrane associated antigens on tumor cells. Responding lymphoid cells shall then be fractionated in an attempt to identify other sub-populations of cells with the ability to suppress the response of other lymphoid cells to the same and/or different antigens after adoptive transfer to syngeneic hosts. When suppressor fractions are identified, they shall be further classified as T cells, B cells, or macrophages, on the basis of surface antigens or adherence properties. A comprehensive study shall be made of the factors responsible for generation of suppressor T cells.